FOODS IN NUTRITION 175 



through the system as circulating or tissue proteid is only an 

 accident provided the supply be above the demand of the 

 cells for tissue proteid; these demands are the first to be 

 supplied by the nitrogenous material at hand. 



From this it is not to be inferred that the exigencies of nu- 

 trition will be met as well without as with circulating pro- 

 teid. When the diet consists of just enough proteid to 

 supply the tissue wastes and of ample carbohydrate and hy- 

 drocarbon materials, the nutritive process is impaired. It 

 seems necessary to perfect health that the supply of nitro- 

 genous food be sufficient to allow for the oxidation of some 

 of it as circulating proteid in a manner analogous to oxida- 

 tion of the non-nitrogenized materials. Life can be main- 

 tained on nitrogenous food alone, but it is obvious that when 

 this is done the amount of circulating proteid must be enor- 

 mously increased so that it may be oxidized to furnish energy 

 for the body; for those substances, the oxidation of which 

 corresponds to oxidation of circulating proteids and which 

 furnish the main supply of energy for doing work (viz., the 

 carbohydrates and hydrocarbons), are now withdrawn from 

 the economy. It follows, conversely, that the ingestion of 

 carbohydrates and hydrocarbons lessens the amount of pro- 

 teid necessary to nutrition. 



The albuminoids, such as gelatin (not meant to be in- 

 cluded under the term "nitrogenous" foods, though they con- 

 tain nitrogen), cannot take the place of tissue proteid; they 

 may be burnt in lieu of the circulating proteids and supply 

 energy just as the carbohyrdates and fats do. 



It is to be remembered that any excess of proteid or al- 

 buminoid food is not discharged as such in the excreta, but 

 undergoes oxidation, the end products of which are always 

 the same, water, carbon dioxide and urea, or related sub- 

 stances ; the development of heat is also an invariable accom- 

 paniment of their destruction. 



While a person may live on proteid food, the amount 

 necessary taxes the digestive and excretory organs to such 



